Learn / Duplicate variants

Fix duplicate variants in Shopify CSV imports

Duplicate variant rows are a common reason Shopify imports fail. Keep one row per unique Handle + Variant SKU combination.

1. 1. Sort by Handle and Variant SKU.
2. 2. Remove repeated combinations, keep the intended final row.
3. 3. Recheck price, inventory, and required fields after dedupe.
4. 4. Upload the updated file for validation.